The source of nutrients to a post-hatch bird changes as the embryonic yolk is replaced with an exogenous diet. The hatchling must switch from a yolk nutrient-based diet (mainly fats) to a solid feed diet (mainly carbohydrates and proteins). Birds hatch with an immature gastrointestinal tract—indeed, with the yolk sac still attached. After hatch, the gastrointestinal tract undergoes rapid morphological, biochemical and cellular development in order to assimilate ingested nutrients. Since the intestine is instrumental in supplying the precursors for growth, its development plays an important role in the animal's ultimate ability to grow, gain weight, utilize dietary nutrients, and resist enteric disease pathogens.
All oviparous species hatch with an underdeveloped capacity to digest dietary constituents; accordingly, hatchling growth and enteric disease resistance are greatly suppressed. Post-hatch development of this digestive capacity is facilitated by exposure of enteric tissue to dietary constituents, but is often compromised by various environmental factors that act upon the hatchling. It is desirable to enhance the digestive capacity of the animal before hatch, because there are few environmental factors that can compromise enteric development during incubation. Moreover, because shorter incubation time and weak hatchlings are observed in a number of situations (e.g., when eggs are produced by young hens), there remains a need for new ways to stimulate the enteric development and growth of birds after hatch.
Examples of substances which have been introduced into embryonated poultry eggs via in ovo administration include live culture vaccines, antibiotics, vitamins, and competitive exclusion media. See generally, U.S. Pat. No. 6,244,214 to Hebrank. Specific examples of treatment substances are described in U.S. Pat. No. 4,458,630 to Sharma et al., and U.S. Pat. No. 5,028,421 to Fredericksen et al. See also, U.S. Pat. No. 4,458,630 to Sharma et al., U.S. Pat. No. 4,681,063 to Hebrank, and U.S. Pat. No. 5,158,038 to Sheeks et al. However, the introduction of treatment substances in ovo in order to enhance enteric development and overall growth of an animal has heretofore not been described.